TEEN MOM RAPE SHOCKER

"Gary Shirley raped MY daughter!" That's the shocking claim of Teen MomAmber Portwood's anguished father - who rips the lid off the deepest secrets of her dysfunctional childhood and violent relationship with baby daddy Gary Shirley.

In an amazingly candid exclusive ENQUIRER interview, Shawn Portwood says he believes his daughter Amber began having sex with Gary when she was just 15, which if true could constitute "statutory rape" and therefore Gary could have been tossed in jail!

But even before she became a reality TV train wreck, Amber was physically and emotionally abused, and she was devastated when her younger sister died of Sudden Infant Death Syndrome, her dad says.

Amber - whose 2-year-old daughter with Gary, Leah, was briefly taken away from her - now faces prison time for pummeling Gary on an episode of the popular MTV series.

But Portwood blames Gary for his 20-year-old daughter's downward spiral.

"Gary got Amber pregnant as a means of controlling her. He was terrified that she would leave him. He used to pick her up from school and just not bring her back," Portwood told The ENQUIRER.

According to Portwood, he believes the couple began having sex when Gary was 19 and Amber was 15 - which, if true, could be a violation of law in their home state of Indiana, and Gary could have been charged with statutory rape.

"Amber and Gary told me that they waited until she was 16 to start having sex and she got pregnant the first time, but Ithink they were lying," Portwood told The ENQUIRER.

"They'd been going together for over a year by then, and if I had known Gary was having sex with my daughter, I would have killed him!"